Explain to me about Non Resistor Spark plugs please ???

poormansporsche

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Morning,

My early C230K needs the Non Resistor type spark plugs but the post facelift C230K has resistor type spark plugs.

I went to MB to buy a new set of leads as mine are degrading somewhat (the car hunts a bit when you touch them) but the part is NLA as a whole - they will sell plugs and wires seperately and you have to build it yourself. There is some notice on the system about using the later leads but the parts man couldnt work it out.

So am I right in assuming that in my car the resistors are in the leads themselves and in the later leads are resistor free ?

I have a whole set of later leads here, could i use them with resistor type spark plugs (which i also have ?)

The coil packs for both early and later cars have the same part number ??


Any thoughts will be appreciated


Cheers
 

carat 3.6

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Yes, and yes.

As long as you have only one set of resistors, it doesn't matter if they are in the leads or the plugs.
 

Ted

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I don't believe you need resistive cables or plugs.
Their only purpose is to prevent radio interference (or tv interference as you pass tv aerials).
 

E55BOF

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Depends how much you listen to the radio, and whether you care about interfering with other people's radio and TV reception. I do both.
 

Ted

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The suppression is usually built in at source. The bonnet, wings etc also dampen interference such that it will not interfere with TVs. (Try tuning off station, and then lifting the bonnet)
Resistive cables and particularly plugs are a 'quick fix' to prevent or reduce interference to your car radio.

You do of course have them on your bike? Motorbikes are the worst offenders for ignition generated interference on TVs due to the engine being exposed. :)
 
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poormansporsche

poormansporsche

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I'm not sure if I've got it round the wrong way or not but the car konked out with the later (what I thought were non resistor) leads in conjunction with the early (non resistor) spark plugs. Was mostly fine when I put the original leads back in !
 

hotrodder

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Possibly because the main reason for suppressing EMI (electromagnetic interference which includes RF, radio frequencies) is to stop the ignition system interfering with the engine management... lots of sensors using less than 12V a few inches away from ignition components kicking out 40+ kV pulses

While adding resistors helps with EMI they also subtly alter spark characteristics in kinda the same way that playing with plug gaps does, IIRC increasing the total resistance (say with resistor plugs and the wrong type of HT lead*) is akin to increasing the plug gap

* Distributed resistance, inductance or fixed resistance (like resistors in the connectors at the ends of the leads)
 

E55BOF

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Resistive cables and particularly plugs are a 'quick fix' to prevent or reduce interference to your car radio. You do of course have them on your bike?

Yes, on all four of them.
 

190

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Adding more than stock resistance to the ignition path will in theory reduce spark energy slightly but with an electronic ignition system it's unlikely to be noticed it just reduces the margin slightly. Non resistor plugs are becoming less common so if you are concerned you might be better building up new leads using solid copper ignition lead and then use resistor plugs.

Anyone running points on an old car though should definitely steer clear of additional resistance as it has more of an impact with the lower energy ignitions. Some will tell you that an additional 5-10,000 ohms is nothing compared to the almost infinite resistance of the spark plug gap but that's misleading because once the spark is created the ionised path in the plug gap has a measurable resistance which then means the extra 5- 10,000 ohms is significant on a low energy ignition system. It's just ohms law which means some of the ignition voltage will be dropped across any resistance in the ignition path.
 

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